Gear and shaft assemblies come in various configurations. For example, planetary gear sets, typically include a sun gear, a ring gear, a pinion carrier, and at least one pinion (also known as a planet gear). A simple planetary gear set may have one pinion rotatably mounted to the pinion carrier, while a compound planetary gear set may have a plurality of pinions rotatably mounted to the pinion carrier. Each pinion is rotatably mounted to the pinion carrier through a pinion shaft coupled to the pinion carrier. The pinion carrier may revolve around the sun gear's axis of rotation or may be stationary.
Planetary gear sets are typically part of a larger mechanical assembly, such as a transmission for a work machine. Planetary gear sets allow a device to adjust the speed and torque of an output shaft by adjusting a gear ratio between an input shaft and the output shaft. This may be accomplished by locking one of the gears, such that it is stationary with respect to a shaft it is rotatably mounted to, or by selecting a second set of gears in a stacked planetary gear set. For example, the sun gear may be held stationary, while the pinion and ring gear are allowed to freely rotate, the pinion may be held stationary, allowing the sun and ring gears to rotate, or the ring gear may be held stationary, allowing the sun gear and pinion to rotate. Each combination of rotating and stationary gears results in a different gear ratio between the input and output shafts. Alternatively, by locking two gears, such as the sun and ring gears, the ring gear and the pinion, or the pinion and the sun gear, will cause the entire planetary gear set to rotate together. This results in the rotational speed of the input and output shafts being equal.
A common problem in planetary gear sets is how to cost effectively constrain the pinion shaft from moving axially and rotationally with respect to the pinion carrier. Constraint of the pinion shaft can be especially challenging when lubricating fluid is provided to the pinion bearings by pressure. For example, high lubricating fluid pressure may axially push on the pinion shaft. Rotation of a poorly lubricated gear may apply torque to the gear shaft, which may result in additional wear, such as to the gears, shafts, and bearings, and/or improper alignment between the pinion and the ring and/or sun gears. High rotational speed applications further require the constraining method to be robust. Further complications arise in a planetary gear set with a low profile, which can be packaged into a compact envelope.